Preparation of magnetic particles by reacting iron,cobalt,or nickel salts with phthalate ion in dialkyl sulfoxide

ABSTRACT

A METHOD FOR PREPARING FINELY DIVIDED MAGNETIC METAL PARTICLES BY DISSOLVING A METAL SALT OF NICKEL, COBALT, IRON, OR MIXTURES OF THESE IN A DIALKYL SULFOXIDE BATH, PREFERABLY DIMETHYL SULFOXIDE; REACTING WITH PHTHALATE ION IN SAID BATH; PRECIPITATING THE METAL PHTHALATE REACTION PRODUCT BY ADDING WATER TO THE BATH; SEPARATING THE PRECIPITATE; HEATING AND REDUCING WITH HYDROGEN AT ELEVATED TEMPERATURES TO PRODUCE METALLIC PARTICLES OF CUBIC STRUCTURE IN A FINE PARTICLE SIZE RANGE OF ABOUT .01 MICRON TO ABOUT 7 MICRONS, WHICH ARE USEFUL IN MAGNETIC RECORDING MEDIA AND FOR PREPARING PERMANENT MAGNETS, MAGNETIC CORES, AND MAGNETICALLY RESPONSIVE FLUID COMPOSITIONS AS ARE EMPLOYED IN MAGNETIC CLUTCHES AND THE LIKE. PRECIPITATION OF THE METAL PHTHALATE IS NOT ACHIEVED IF AQUEOUS SOLUTIONS OF METAL SALT AND PHTHALATE ION ARE MIXED AND DIALKYL SULFOXIDE IS ADDED THEREAFTER.

United States Patent O US. Cl. 117-235 12 Claims ABSTRACT OF THEDISCLOSURE A method for preparing finely divided magnetic metalparticles by dissolving a metal salt of nickel, cobalt, iron, ormixtures of these in a dialkyl sulfoxide bath, preferably dimethylsulfoxide; reacting with phthalate ion in said bath; precipitating themetal phthalate reaction product by adding water to the bath; separatingthe precipitate; heating and reducing with hydrogen at elevatedtemperatures to produce metallic particles of cubic structure in a fineparticle size range of about .01 micron to about 7 microns, which areuseful in magnetic recording media and for preparing permanent magnets,magnetic cores, and magnetically responsive fluid compositions as areemployed in magnetic clutches and the like. Precipitation of the metalphthalate is not achieved if aqueous solutions of metal salt andphthalate ion are mixed and dialkyl sulfoxide is added thereafter.

FIELD OF THE INVENTION This invention relates to the manufacture of finemagnetic particles suitable for use in magnetic recording media,permanent magnets, magnetic cores, and in magnetically responsive fluidsuspensions, such as magnetic or electrostrictive clutch coupling andthe like.

SUMMARY OF THE INVENTION More particularly, the invention relates to amethod of making fine magnetic metal, alloy, or oxide particles bydissolving a metal salt of nickel, cobalt, iron, or mixtures of thesesalts in a dialkyl sulfoxide bath (preferably dimethyl sulfoxide);reacting the metal salt with phthalate ion which is dissolved in thedialkyl sulfoxide bath; precipitating the metal phthalate reactionproduct by adding water to the bath; separating the precipitate; anddecomposing the precipitate, either by heating in an oxidizingatmosphere at 100-450" C. for a period of time sufiicient to removeorganic matter and provide a magnetic oxide, or by reducing theprecipitate or the oxide formed by the precipitate with hydrogen atelevated temperatures to produce metallic particles of cubic structurein fine particle size varying between about 0.01 micron to about 7microns.

During the water dilution-precipitation step which follows thecombination of phthalate ion and metal salt in the dialkyl sulfoxidebath, it may be advantageous to employ an ultrasonic field which aids incrystallizing single metal salts or co-crystallizing mixtures of metalsalts and in producing the metal phthalate in very fine and uniformparticle size range which, in turn, leads to superior magnetic results.

The ultrasonic field may be formed by commercially available devices,such as the Rapisonic ultrasonic device sold by Sonic EngineeringCorporation, Stamford, Conn., which vibrates a blade at a frequency of22K c.p.s., or by piezoelectric crystal transducers (e.g., quartz,barium titanate, and the like which convert electric energy intoultrasonic waves between 10K c.p.s. and 1M c.p.s.), or by othertransducers which are described in the literaice ture. Low intensitiesof the order of .01-0.7 watt per square centimeter of ultrasonic energyare generally adequate to disperse the precipitate and prevent particleagglomeration by vibrational motion in the dialkyl sulfoxide bath.

The phthalate ion may conveniently be provided from monobasic solublesalts of phthalic acid, such as sodium acid phthalate, potassium acidphthalate, ammonium acid phthalate; from soluble dibasic salts ofphthalic acid, such as disodium phthalate, dipotassium phthalate,diammonium phthalate; from phthalic anhydride; or from phthalic acid.

Any soluble salt of iron, cobalt, or nickel may be used, and thechlorides, nitrates, sulfates, and acetates are representative saltswhich are readily available and have been used with good results.

It is preferred to use a dilute solution of a metal salt in a dialkylsulfoxide bath and to add the phthalate to it in diluted form, also indialkyl sulfoxide. For convenience and easy control, fractional molarquantities are mixed by preparing separate solutions of salt in dialkylsulfoxide and of phthalate ion in dialkyl sulfoxide.

If similar amounts of metal salt or of phthalate ion are dissolved inwater instead of in dialkyl sulfoxide and mixed, no precipitation isobserved. If the same amount of dialkyl sulfoxide is added to such awater solution as was used in the method of the invention, there is nochange and no precipitation occurs.

In short, an essential feature of the method of the present invention isthe dialkyl sulfoxide bath as the medium for dissolving the metal saltand phthalate ion in the sequence of first dissolving and thenprecipitating the metal phthalate by adding water.

For reasons of economy and availability, dimethyl sulfoxide is thepreferred dialkyl sulfoxide, but diethyl sulfoxide, dipropyl sulfoxide,dibutyl sulfoxide, and diisobutyl sulfoxide may be used. Unsymmetricalsulfoxides may be used, such as methyl ethyl sulfoxide and methylisobutyl sulfoxide.

The foregoing and other objects, features, and advan tages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples aregiven by way of pointing out critical aspects of the invention andpreferred embodiments.

Example 1A.Criticality of dialkyl sulfoxide bath as the medium forreacting phthalate ion and metal salt in the absence of water Solutionsof one-tenth molar C001 6H O and FeCl 4H O in water and in dimethylsulfoxide were prepared.

One-tenth molar solutions of potassium acid phthalate in water and indimethyl sulfoxide were prepared.

Equal volumes of the above 0.1 molar ferrous chloride in water and 0.1molar phthalate solution in water were mixed. No precipitation wasobserved.

A volume of dimethyl sulfoxide equal to that of the 0.1 molar ferrouschloride and 0.1 molar potassium acid phthalate was added to the aqueousmixture and no precipitation was observed.

Equal volumes of the above 0.1 molar ferrous chloride in dimethylsulfoxide and 0.1 molar potassium acid phthalate in dimethyl sulfoxidewere mixed. No precipitate was formed. A volume of Water twice that ofthe volume of ferrous chloride and potassium acid phthalate solution wasadded and the solution was agitated manually, and the metal phthalatesalt precipitated.

A mixture of equal parts by volume of 0.1 molar cobalt chloride indimethyl sulfoxide and 0.1 molar ferrous chloride in dimethyl sulfoxidewas reacted with an equal volume of 0.1 molar potassium acid phthalatesalt and the co-crystallized cobalt-iron phthalates were precipitated byadding water in a volume equal to the volume of the reaction mixture.

The iron phthalate salt and the mixed iron-cobalt phthalate saltprepared above Were separated by filtration and the residue was washedwith water and placed in an oxidizing atmosphere in a furnace at 400 C.for 3 hours. In each instance, all of the organic matter of theprecipitate was removed and a finely divided magnetic oxide wasobtained; e.g., iron oxide in the form of black gamma iron oxide, andblack flakes of cobalt-modified oxide, respectively.

These two magnetic oxide samples were then placed in a furnacemaintained at a temperature of 260 C. and hydrogen reducing gas waspassed over them for 2 hours to convert the oxide particles to thecorresponding metal and alloy particles. All of the reduced particleswere magnetic, cubic in shape, and ranged in size from about 0.01 toabout 6.1 microns.

Example 1B.Effect of ultrasonic vibrations on diminishing size ofresulting magnetic oxide and metal particles The precipitations indimethyl sulfoxide of the two samples of salts as above (iron andiron-cobalt mixture) were repeated, using an 800 k.c. quartzpiezoelectric transducer to provide an ultrasound field during thedilution-precipitation step. The resulting oxide particles, afterheating in the furnace, were much smaller than those which had beenproduced in the absence of the ultrasonic field. After hydrogenreduction at 260 C. for 2 hours, as above, the particle size ranged from0.01 to 1.0 micron. The average particle size of the iron particles was0.03 micron, and the average particle size for the mixed ironcobaltparticles was 0.04 micron.

Example 2.Effect of variations in concentration of metal salt solutionsin dimethyl sulfoxide This example illustrates the doubling of the metalsalt concentration from 0.1 molar to 0.2 molar. The beneficial resultsof this example are achieved with increasing concentrations as high as0.9 molar. At higher concentrations, additional washing is necessary andcontrol of uniformity of particle size is more difficult to maintainunder conditions of normal manual agitation.

In general, the same procedure was followed as in Example 1A above and 8g. of FeCl .4H O were dissolved in 200 ml. of dimethyl sulfoxide to forma 0.2 molar solution. Eight g. of potassium acid phthalate weredissolved in 200 ml. of dimethyl sulfoxide to form a 0.2 molar solution.These solutions were mixed and no reaction occurred. 300 ml. ofdistilled water was added, causing precipitate to form which was allowedto settle overnight. The supernatant liquid was siphoned off and theprecipitate washed with 1000 ml. of distilled water. This washingprocedure was repeated six times and the precipitate was then removed bycentrifuging, dried at 100 C. for 54 hours, and then reduced in a nickelboat under hydrogen at 400 C. for 2 hours. The metal particles recoveredwere cubic in form, varied in particle size between 0.01 and 0.1 micron,and had an average particle size of 0.03 micron.

The following magnetic properties were observed when run on theVibrating Sample Magnetometer (VSM) at an applied field strength of 4000oersteds:

Ms 4000 oe.-134 emu. (electromagnetic units per g.) Hc-547 e. Mr/ Ms0.33

1 Squa reness ratio.

4 Example 3.Preparation of mixed cobalt-iron magnetic particles A 0.2molar solution of mixed cobalt and iron salts was prepared by dissolving9.6 g. of CoCl .6H O and 8.0 g. of FeCl- .4H O in 200 ml. of dimethylsulfoxide. A 0.2 molar phthalate solution was prepared by dissolving 12g. of potassium acid phthalate in 300 ml. of dimethyl sulfoxide. Themixed salts in solution were added without reaction to the phthalatesolution with efficient agitation, and 800 ml. of distilled water wasthen added to cause precipitation. The precipitate was allowed tosettle; the supernatant liquid was siphoned off; and the material waswashed six times with distilled Water, 1000 ml. of distilled water beingused in each washing. After the sixth washing, the wet concentratedwater slurry was centrifuged and the precipitate was removed and driedat C. for 54 hours. The product was then put in a nickel boat, reducedat 400 C. under hydrogen for 2 hours, and cubic crystals of magneticcobalt-iron in a particle size range of from 0.02 to 5.8 microns wereproduced. The average particle size was 1.5 microns. By testing on theVSM, the following magnetic characteristics were determined:

Example 4.Preparation of mixed nickel-iron magnetic particles A 0.2molar solution of mixed nickel and iron salts was prepared by dissolving9.6 g. of NiCl .6H O and 8 g. of FeCl AH O in 200 ml. of dimethylsulfoxide. A 0.2 molar solution of phthalate was prepared by dissolving12 g. of potassium acid phthalate in 300 m1. of dimethyl sulfoxide. Themixed salts in solution were added without reaction to the phthalatesolution with efiicient agitation, and 800 ml. of distilled water wasthen added to cause precipitation. The precipitate was allowed tosettle; the supernatant liquid was siphoned off; and the material waswashed six times with distilled water, 1000 ml. of distilled water beingused in each washing. After the sixth washing, the wet concentratedwater slurry was centrifuged and the precipitate was removed and driedat 100 C. for 54 hours. The product was then put in a nickel boat,reduced at 400 C. under hydrogen for 2 hours, and cubic crystals ofmagnetic nickel-iron in a particle size range of 0.01 to 0.5 micron wereproduced. The average particle size was 0.1 micron. By testing on theVSM, the following magnetic characteristics were determined:

Ms 4000 oe.- emu. Hcl96 oe. Mr/Ms-0.1

Example 5.-Addition of powdered phthalic acid to dimethyl sulfoxide A0.2 molar solution of mixed nickel and iron salts was prepared bydissolving 9.6 g. of NiCl .6H O and 8 g. of FeCI AH O in 200 ml. ofdimethyl sulfoxide. 16 g. of powdered phthalic acid was added to thesolution of nickel and iron salts in the dimethyl sulfoxide bath withagitation. No precipitate formed.

There was then added 1800 ml. of distilled water to cause precipitation.The precipitate was allowed to settle; the supernatant liquid wassiphoned 01f; and the material was washed six times with distilledwater, 1000 ml. of distilled water being used in each washing. After thesixth washing, the wet concentrated water slurry was centrifuged and theprecipitate was removed and dried at 100 C. for 54 hours. The productwas then put in a nickel boat, reduced at 400 C. under hydrogen for 2hours, and cubic crystals of magnetic nickel-iron in a particle sizerange of 0.01 to 0.1 micron were produced.

The average particle size was 0.04 micron. By testing on the VSM, thefollowing magnetic characteristics were determined:

Ms 4000 oe.--159 emu. H -463 oe. Mr/Ms-0.3

Example 6-Preparation of 70% iron30% cobalt A 0.1 molar solution of70:30 iron-cobalt was prepared by dissolving 6.73 g. FeCl .4H O and 3.27g. of

CoCl .6H2O

in 500 ml. of dimethyl sulfoxide. A 0.1 molarphthalate ion solution wasprepared by dissolving 10.2 g. of monopotassium phthalte in 500 ml. ofdimethyl sulfoxide. These 500 ml. solutions were mixed together withoutreaction, and 1000 ml. of distilled water was added while agitating tocause precipitation. An additional 1000 ml. was added to insure completeprecipitation. The precipitate was alloweed to settle; the supernatantliquid was siphoned off; and the material was washed twice withdistilled water, 1000 ml. of distilled water being used in each washing.After the second washing, the concentrated water slurry was centrifugedand the precipitate was removed. The product was heated at 400 C. 14hours, whereby organic matter was eliminated and a magnetic cobaltmodified iron oxide was produced. The magnetic oxide was reduced in afurnace at 260 C. with hydrogen for 2 hours and the resulting alloy hadthe following magnetic characteristics:

Ms 4000 oe.--109 emu.

Hc--303 oe.

Example 7.-Preparation of 60% iron40% cobalt A 0.1 molar solution wasprepared by dissolving 6.05 g. of FeCl .4H O and 4.59 g. of CoCl .6H Oin 500 ml. of dimethyl sulfoxide. A 0.1 molar solution of phthalate ionwas prepared-by dissolving 10.2 g. of potassium acid phthalate in 500ml. of dimethyl sulfoxide. These 500 ml. solutions were mixed togeherwithout reaction and 1000 ml. of distilled water was added whileagitating to cause precipitation. An additional 1000 ml. of distilledwater was added to insure complete precipitation. The precipitate wasallowed to settle; the supernatant liquid was siphoned ofi; and thematerial was washed twice with distilled water, 1000 ml. of distilledwater being used in each washing. After the second washing, theconcentrated water slurry was centrifuged and the precipitate wasremoved. The product was heated at 400 C. 14 hours, whereby organicmatter was eliminated and a magnetic cobalt modified iron oxide wasproduced. The magnetic oxide was reduced in a furnace at 260 C. withhydrogen for 2 hours to produce a magnetic alloy.

Example 8.Preparation of magnesium modified ironparticles with phthalicacid addition In 200 ml. of dimethyl sulfoxide, there were dissolvedwithout reaction '16 g. of FeCl .4H O, 4 g. of

and 16 g. of phthalic acid. A volume of distilled water which was fivetimes that of the dimethyl sulfoxide (e.g., 1000 ml.), was added withagitation to cause precipitation. The precepitate was washed and thewash liquor was removed by siphoning and centrifuging. The centrifugedmaterial was again washed and dried overnight in an oven at 100 C., andreduced with hydrogen in a tube furnace at 400 C. for 2 hours to producea magnetic alloy of iron and magnesium.

Example 9.-Preparation of iron-cobalt-magnesium particles with phthalicacid addition In 200 ml. of dimethyl sulfoxide, there were dissolvedwithout reaction 8 g. of FeCl .4I-I O, 9.6 g. of

COC12 .6H3O

4 g. MgCl .6H 0, and 16 g. of phthalic acid. A volume of distilled waterwhich was five times that of the dimethyl sulfoxide (e.g., 1000 ml.) wasadded with agitation to cause precipitation. The precipitate was washedand the wash liquor was removed by siphoning and centrifuging. Thecentrifuged material was again washed and dried overnight in an oven at100 C., and reduced with hydrogen in a tube furnace at 400 C. for 2hours to produce a magnetic alloy of iron-cobalt-magnesium.

The products from Examples 8 and 9 were combined and gave the followingvalues for the magnetic characteristics Ms 4000 oe.-114 emu. Hc417 oe.Mr/Ms0.23

Example 10.*Iron particles from ferrous sulfate and phthalic acid To 100ml. of diethyl sulfoxide, there was added 8 g. of FeSO -7H O and 8 g. ofphthalic acid and the solution was mixed for 45 minutes at roomtemperature without reaction. The solution was diluted with 1000 ml. ofdistilled water to precipitate the insoluble iron salt which was washedtwice with 1000 ml. portions of distilled water, centrifuged, dried at100 C. overnight, and reduced with hydrogen at 400 C. for 2 hours,whereby cubic crystals of magnetic iron where recovered.

The foregoing examples illustrate the wide range of volume proportionsof precipitating water relative to the dialkyl sulfoxide bath; e.g.,from proportions of 1:1 to about 10:1. Larger water volumes may be used(in proportions of 20:1, 40: 1, 50:1, etc.), but it is obviouslyimpractical and contrary to sound washing practice to employ such alarge excess water volume as to risk mechanical loss of the precipitatewhich is in very finely divided form.

In preparing magnetic recording media, the gamma iron oxide or cobaltmodified gamma iron oxide in acicul ar form obtained when the process asin Example 1A included an oxidation step, but no reduction step, may beused together with a film-forming binder.

Mixtures of iron-cobalt metal particles prepared in Example 1 may beused with a binder in the preparation of magnetic recording media, orthe iron particles prepared in Example 2 may be used for sound recordingtape and, similarly, the metal particles of the remaining examples arealso useful in preparing various recording media; especially theiron-cobalt-nickel particles obtained by mixing the products of Examples4 and 6.

Typical, but not limiting, binders for these various recording media arepolyesters, cellulose esters and ethers, vinyl chloride, vinyl acetate,acrylate and styrene polymers and copolymers, polyurethanes, polyamides,aromatic polycarbonates (as, for example, those produced from 2,2 bis(4-hydroxyphenyl)propane), and polyphenyl ethers (as, for example, thoseproduced by oxidative coupling of 2,6 dimethyl phenol).

In addition to dialkyl sulfoxides, a wide variety of solvents may beused for forming a dispersion of the fine particles and binders. Organicsolvents, such as ethyl, butyl and amyl acetate, isopropyl alcohol,dioxane, acetone, methylisobutyl ketone, cyclohexanone, and toluenefrequently are used for this purpose. The particlebinder dispersion maybe applied to a suitable substrate by roller coating, gravure coating,knife coating, extrusion or spraying of the mix onto the backing or byother known methods. The specific choice of non-magnetic support,binder, solvent, or method of application of the paring magnetic recordmedia such as video tapes, computer tapes, and sound tapes.

In preparing recording media, the magnetic particles comprise about40-90% by weight of the film layer applied to the substrate. Thesubstrate is usually a paper, polyester, or cellulose acetate material,although rigid base material of plastic or metal is more suitable forsome uses.

In preparing magnetic cores and permanent magnets, the products of theforegoing examples are mixed with non-magnetic plastic or filler in anamount of 33 to 50% by volume of the finished magnetic metal, theparticles aligned in a magnetic field, and the mixture pressed into afirm magnet structure. Alignment of the particles may be accomplished inan externally applied D.C. magnetic tfield of about 4000 gauss or more,and fields up to 28000 gauss may be used. Pressures may vary widely informing the magnet, and pressures up to 100,- 000 p.s.i. have been usedcommercially.

In preparing fluid magnetic compositions, the magnetic particlesprepared in accordance with the invention may be mixed with hydrocarbonmineral oil or with other liquids as disclosed in Winslow, US. Pat.2,417,850, and Rabinow, US. Pat. 2,575,360. The oil-diluted magneticcomposition responds to a magnetic field and is useful in powercouplings and clutches.

While there has been described and pointed out the fundamental novelfeatures of the invention as applied to preferred embodiments, it willbe understood that various omissions and substitutions and changes inthe form and details of the invention illustrated may be made by thoseskilled in the art without departing from the spirit of the invention.It is therefore the intention thereof to be limited only as indicated bythe scope of the following claims.

What is claimed is:

1. A method for manufacturing magnetic particles comprising:

dissolving salt including a metal salt of nickel, cobalt,

iron, and mixtures thereof in a bath containing dialkyl sulfoxide;

reacting with phthalate ion dissolved in said bath;

precipitating the metal phthalate by adding water to the bath;

separating the precipitate; and

reducing the precipitate with a reducing gas at elevated temperatures torecover finely divided metal particles.

2. A method as claimed in claim 1, wherein said reducing step is carriedout at temperatures between about 225 and 450 C. with a reducing gasselected from the group consisting of hydrogen and carbon monoxide andsaid magnetic particles are produced in the form of crystals of cubicstructure in a particle size range of .01 micron to about 7 microns.

3. A method as claimed in claim 1 wherein said salt includes an ironsalt.

4. A method as claimed in claim 3 wherein said salt includes a nickelsalt.

5. A method as claimed in claim 3 wherein said salt includes a cobaltsalt.

6. A method as claimed in claim 1 wherein said phthalate ion is derivedfrom a monobasic salt of phthalic acid.

7. A method as claimed in claim 1 wherein said phthalate ion is derivedfrom phthalic acid.

8. A method as claimed in claim 1 wherein said phthalate ion is derivedfrom phthalic anhydride.

9. A method for manufacturing magnetic oxide particles comprising:

dissolving salt including a metal salt of nickel, cobalt,

iron, and mixtures thereof in a bath containing dialkyl sulfoxide;

reacting with phthalate ion dissolved in said bath;

precipitating the metal phthalate by adding water to the bath;

separating the precipitate; and

heating the precipitate at -450" C. in the presence of oxygen to removeorganic matter.

10. A method as claimed in claim 1 wherein said dialkyl sulfoxide bathconsists essentially of dimethyl sulfoxide.

11. A method of manufacturing magnetic recording media comprising:

dissolving salt including a metal salt of nickel, cobalt,

iron, and mixtures thereof in a bath containing dialkyl sulfoxide;

reacting with phthalate ion dissolved in said bath;

precipitating the metal phthalate by adding water to the bath;separating the precipitate; reducing the precipitate with a reducing gasat elevated temperatures to recover finely divided metal particles;

adding a non-magnetic binder to said magnetic particles in a solvent forthe binder to form a dispersion;

coating a base with said dispersion; and

drying the coating.

12. A method of manufacturing magnetic recording media comprising:

dissolving salt including a metal salt of nickel, cobalt,

iron and mixtures thereof in a bath containing dialkyl sulfoxide;reacting with phthalate ion dissolved in said bath; precipitating themetal phthalate by adding water to the bath;

separating the precipitate;

heating the precipitate at IOU-450 C. in the presence of oxygen toremove organic matter;

adding a non-magnetic binder to said magnetic particles in a solvent forthe binder to form a dispersion; coating a base with said dispersion;and

drying the coating.

References Cited UNITED STATES PATENTS 3/1962 Fukuda et al. l481059/1965 Miller et al. l48l05 L. DEWAYNE RUTLEDGE, Primary Examiner W. W.STALLARD, Assistant Examiner

